Actually, looking at webcomics that depict PCs as played by (fictional) players, such as DM of the Rings, Darths & Droids or the unfortunately dead Chainmail Bikini, having players join and leave is perfectly possible.

In OotS, we only see the characters' side, in CB we saw both sides and in the two screencap comics listed we only see the characters' side but it's the players' side we hear.

So that means that we don't know what happens on the players' side in OotS. They might as well be effectively non-existent since they don't matter. The comic doesn't delve on the interactions between players, only on the characters.

(Nota bene: I used "character" in the RPG sense because, of course, DM and players are also characters in the story sense.)